Longitudinal Cracking and Spalling in Long Span Post Tensioned Bulb-Tee Girders

摘要

In the study, full-scale field tests and a number of finite element models wereused to investigate the longitudinal cracking and spalling in long span Florida bulb-t girders. The full-scale test consisted of two (2) 75 foot long bulb-t girders which were constructed to form a 150 foot long continuous girder. The instrumentation plan was developed after an analytical study of the bulb-t girder. Fifty-seven (57) internal strain gages were placed in high stress regions prior to concrete casting. Prior to testing, forty-four (44) additional strain gages were mounted to the surface of the girder. The gages were monitored during the post-tensioning of the strands in each duct, as the live loads were applied and during the grouting of the ducts. The FEA modeling consisted of two-dimensional and three-dimensional models. The two-dimensional models were used to examine the effects of various types of the bulb-t girders. Ducts manufactured with either high density polyethylene or galvanized steel were examined. Also, ducts with a round or oval shapes were examined. The four ducts analyzed in the two-dimensional models were oval polyethylene, oval steel, round polyethylene and round steel. The forces caused by strand wedging and grouting pressure in bulb-t girders were applied to the two-dimensional models. The results indicate that round steel ducts are most effective in reducing strains in the concrete web. Models with oval polyethylene ducts had the highest strains in concrete web. The three-dimensional models were used to compare the stresses and deflections in full-scale girders. The three-dimensional models were also used to examine any stress concentration that occurs at the end of the transition zone.